Residual strain, surface roughness. and dislocations of Si_(1-x)Ge_(x) alloy layers grown by molecular beam epitaxy on Si(001) substrates at 550℃ have been characterized by x-ray diffraction. atomic force microscopy, and cross-sectional transmission electron microscopy (XTEM). Two kinds of samples were grown. One is a series of Si_(1-x)Ge_(x) alloy layers with x≤0.3 and a thickness of 5000 A directly grown on Si(001) substrates. and the other is a series of Si_(0.7)Ge_(0.3) alloy layers with a thickness of 2000 A grown on Si(001) via compositionally graded Si_(1-y)Ge_(y) buffer layers (0≤y≤x). The Ge grading rate g_(r) in the buffer layer. defined by g_(r) Ge/μm. ranged from 22 to 76. In the case of direct growth, the surface morphology changes from a wavy ripple pattem to a cross-hatch pattern with increase in x. and islandlike patterns appear at x=0.3. The residual strain decreases with increase in x. whereas the surface roughness increases with x. In the case of Si_(0.7)Ge_(0.3) alloy layers grown with buffer layers. the surfaces of all samples display cross-hatch pattern. The surface roughness is highest for a grading rate of about 35, and it decreases for both lower and higher grading rates. The residual strain also shows a similar dependence on the grading rate. XTEM images are correlated to the residual strain and surface roughness.
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